Gaseous and liquid fuel industrial furnace burner



March 29, 1966 c. H. EISENTROUT GASEOUS AND LIQUID FUEL INDUSTRIAL FURNACE BURNER Filed Feb. 21, 1964 INVENTOR. CAR L H. EISENTROUT hlS ATTORNEY United States Patent 3,242,966 GASEOUS AND LIQUID FUEL INDUSTRIAL FURNACE BURNER Carl H. Eisentrout, Coraopolis, Pa., assignor to A. M. Byers Company, Ambridge, Pa. Filed Feb. 21, 1964, Ser. No. 346,525 4 Claims. (Ci. 15811) This invention relates to an industrial furnace burner and, more particularly, to a novel combination gas and oil fired burner.

An object of the present invention is to provide a novel burner using lower cost natural gas as the major fuel and oil as the minor fuel, and yet which is able to achieve the luminosity associated with an oil-fired burner by slight cracking of the natural gas to produce luminous particles of carbon.

Another object of the invention is to provide a novel burner assembly which uses combustion chamber stratification to advantage in maintaining a reducing atmosphere on the bath or reheating product with extremely good fuel efficiency (that is, with a very slight deficiency of air).

Another object of the invention is to provide a novel industrial furnace burner which provides excellent atomization of fuel, fast combustion and. heat release at the burner and yet which maintains good heating through the length of the furnace, as well as furnace roof shielding effect, resulting in prolonged furnace roof life.

A still further object of the invention is to provide a furnace burner fired by oil and gas and having controls to instantly vary flame characteristics and to prevent flame blow-off.

Other objects and advantages of the invention will become more apparent from a study of the following description taken with the accompanying drawing wherein:

The single figure is a longitudinal, cross-sectional view of an industrial furnace burner fired by natural gas and oil and embodying the principles of the present invention.

Referring more particularly to the drawing, an industrial furnace burner is shown which is fired by both natural gas and oil.

The burner operates on a ratio of about 70% natural gas to 30% oil, based on B.t.u. input. This ratio may be varied when desired because of a specific application or fuel costs.

The total air required is divided into primary air, duct 1 and secondary air, duct 2. This air may be provided by one blower (not shown) dividing the air into duct 1 and duct 2 with the proportioning of the air between these two ducts controlled by the rod interlocking dampers 3 and 4 located in each duct. As an alternate, the primary and secondary air may each be provided by individual blowers with the air flow controlled by interlocked dampers (similar to those shown) located on the upstream side of the blowers. In either case, it is necessary to provide a gas safety shut off valve (not shown, but which is well known in the art) which will automatically close should the primary air supply fail.

The total (primary plus secondary) air required is determined by the total B.t.u. input and the desired furnace atmosphere (oxidizing, neutral, or reducing) which will vary with each application. The diameters of the primary air duct 1 and flow nozzle 5 are to be sized to handle a maximum primary air based. on the equation: max. primary air (cubic feet/hr.)=.()08 total B.t.u./hr. gas plus cubic feet/hr. gas. Damper 3, controlling the primary air, must be adjustable to provide a minimum primary air based on the equation: min. primary air (cubic feet/ hr.)=.005 total B.t.u./hr. gas plus cubic feet/hr. gas.

The diameter of the secondary air is sized to handle a maximum secondary air flow (cubic feet per hr.)=total air required (determined as stated above by total oil plus gas B.t.u. input and desired furnace atmosphere)-minimum primary air. Damper 4 controlling the secondary air flow is interlocked with damper 3 controlling the primary air flow so that as the primary air flow is increased above minimum primary air, the secondary air flow will be decreased as the difference between total air and primary air, thereby maintaining a constant total fuel to total air ratio.

The total air may be preheated provided the primary air plus gas mixture will not be sufiiciently high in temperature to cause cracking of the gas.

Natural gas (at low or high pressure-15 p.s.i.g. works well) enters the primary air duct through manifold 6 around the perimeter of the duct, through ports 13 and is thoroughly mixed with the primary air. The velocity pressure of this air-gas mixture is increased as it passes through the flow nozzle 5. The mixture then passes through the water cooled jacket 12 and into the furnace at port 7 where ignition begins.

This rich mixture containing a deficiency of air covers the bath or reheating product with an extremely reducing atmosphere. As this air-gas mixture progresses through the furnace, the excess unburned natural gas rises into the secondary air stream where the majority of the combustion is completed by the time the gases reach the furnace stack. The effect of entering a rich gas-air mixture below the secondary air utilizes furnace stratification in a beneficial manner to provide a stratified horizontal level of reducing atmosphere. This prevents excess oxidation of the product while approaching complete combustion, maximum flame temperature and maximum fuel efliciency.

An oil burner 8 is inserted in the secondary airduct. The oil (#6 oil works well) may be atomized by either steam, air or mechanically. Should the atomization be accomplished by air, this additional air must be taken into account when determining total air required. The oil burner is to be sized depending upon total B.t.u. input and the desired percent of oil to total fuel (usually 30%). The oil provides luminosity and overcomes the shortcomings normally associated with a natural gas flame. The secondary air plus atomized oil passes through the water cooled jacket 11 and into the furnace at port 9. The excess of secondary air in relation to the required air for combustion of the oil provides a cooling effect on the furnace roof, does not reach the bath or reheating product (preventing oxidation at that level) and provides the required additional air for the gas in the gas-rich primary air-gas mixture.

Thus it will be seen that I have provided an efficient combination gas-oil burner which is useful as an industrial burner or for homes, having characteristics which are summarized as follows:

Burning 30% #6 crude oil with 70% natural gas (measured on thermal input) produces an excellent luminous flame. There is a drop in flame temperature and heating results with much less than 30% oil. The burner will operate on gas line pressures as low as 15 p.s.i.g.

The natural gas is pre-mixed with the primary air (the ratio of air to gas which varies flame characteristics is controlled by the damper in the secondary air duct). Reduction of this ratio will induce additional cracking of the gas as it is heated above 1200 F. with a deficiency of air. Primary air may be preheated at something less than 1200 F. to prevent cracking of the gas in the pre-miXing chamber.

The secondary air duct with the oil burner is considerably on the oxidizing side. However, this excess air does not reach the bath or reheating product since it combines with the natural gas and burns the gas from the top of the furnace down. The natural gas being lighter than air will rise into the secondary air stream. The net result is firing with a minimum deficiency of air (good economy) while maintaining highly reducing atmosphere on the product being heated.

The pro-mixing of the gas and air results in fast burning (high flame velocity) at the burner. However, the deficiency of primary air pre-mixed with the gas (this ratio is variable and controllable) will extend the flame length resulting in good heating for the length of the furnace. (A rectangular shaped primary air and gas duct can also maintain good flame width particularly when used in conjunction with a rectangular secondary air duct and flat oil nozzle.)

The pro-mixing of primary air and gas gives excellent atomization. The quick heat release of this mixture, also assists in atomization of the fuel oil to a small extent (similar to atomization of oil with high pressure natural gas).

The excess secondary air contributes a cooling effect on the furnace roof. The high velocity of this air results in a shielding blanket (stratification) assisting in lower roof temperature and better roof life.

The damper control for the secondary air will vary the ratio of primary air to gas, thus increasing flame length with a reduction in this ratio, or decreasing flame length with an increase in this ratio. The oil burner may also be adjusted in or out again changing flame characteristics.

The oil burner acts as a pilot to prevent flame blow-off of the natural gas flame.

It is recognized that pure oxygen or oxygen enriched air may be used in place of air in this burner. The equations deter-mining duct sizes are based on using air containing 20% oxygen and thus should any amount of pure 100% oxygen replace a portion of this air, the equations must reflect this change.

While I have illustrated and described a single specific embodiment of my invention, it will be understood that this is by way of illustration only, and that various changes and modifications may be made within the contemplation of my invention and Within the scope of the following claims.

I claim:

1. A furnace burner comprising a primary air duct, a combustible gas source having inlet port means leading into said primary air duct, the terminal end of said primary air duct being in the form of a flow nozzle of reduced diameter, a water jacket surrounding said nozzle, a secondary air duct, a crude oil source having inlet port means leading into said secondary air duct, a damper in each of said air ducts for controlling air flow therein, and linkage means interconnecting said dampers so that as air input is increased in one duct it is decreased in the other.

2. A furnace burner comprising a primary air duct, a combustible gas source having inlet port means leading into said primary air duct, a secondary air duct, a crude oil source having inlet port means leading into said sec ondary air duct, water jackets surrounding the terminal,

exit portions of said primary and secondary air ducts, a damper in each of said air ducts for controlling air flow therein and linkage means interconnecting said dampers so that as air input is increased in one duct it is decreased in the other.

3. A combination gas and oil furnace burner, comprising a primary air duct, a manifold surrounding said duct and having a plurality of spaced inlet ports for introducing combustible gas into said duct, said duct including an outlet of reduced diameter, forming a flow nozzle, a secondary duct extending along said primary duct and having a terminal outlet extending immediately above the terminal outlet of said primary duct, a furnace wall supporting the outlet terminal portions of said ducts so that the terminal portion of said secondary duct is immediately above the terminal portion of the primary duct, water jackets also supported by said furnace Wall and surrounding the respective outlets of said ducts, an oil burner tube extending in said secondary duct in the axial plane of said primary duct, and dampers in said ducts interconnected by linkage means so that as air input is increased in one duct it is decreased in the other.

4. An industrial burner comprising a furnace wall, a primary duct terminating in said wall, an annular water jacket encircled by and enclosed Within the terminal portion of said primary duct and being shaped to form a flow nozzle, a manifold surrounding an intermediate portion of said primary duct and having a plurality of outlets leading into said duct for introducing combustible gas into said duct, a secondary duct extending alongside said primary duct and having an outlet in said wall, a second annular water jacket supported in said wall and surrounding the outlet of said secondary duct, an oil burner extending longitudinally in said secondary duct and terminating adjacent the outlet thereof immediately above said fiow nozzle, a damper in each of said ducts, interlocking control means for said dampers which increase the air input in one duct while decreasing it in the other so as to maintain a substantially constant total fuel to total air ratio.

References Cited by the Examiner UNITED STATES PATENTS 1,707,772 4/ 1929 Robinson.

2,515,843 7/1950 Te Nuyl l581.5 2,851,093 9/1958 Zink et a1. 15811 FOREIGN PATENTS 944,445 12/ 1963 Great Britain.

FREDERICK L. MATTESON, 111., Primary Examiner.

MEYER PERLIN, E. G. FAVORS,

Assistant Examz'ners. 

1. A FURNACE BURNER COMPRISING A PRIMARY AIR DUCT, A COMBUSTIBLE GAS SOURCE HAVING INLET PORT MEANS LEADING INTO SAID PRIMARY AIR DUCT, THE TERMINAL END OF SAID PRIMARY AIR DUCT BEING IN THE FORM OF A FLOW NOZZLE OF REDUCED DIAMETER, A WATER JACKET SURROUNDING SAID NOZZLE, A SECONDARY AIR DUCT, A CRUDE OIL SOURCE HAVING INLET PORT MEANS LEADING INTO SAID SECONDARY AIR DUCT, A DAMPER IN EACH OF SAID AIR DUCTS FOR CONTROLLING AIR FLOW THEREIN, AND LINKAGE MEANS INTERCONNECTING SAID DAMPERS SO THAT AS AIR INPUT IS INCREASED IN ONE DUCT IT IS DECREASED IN THE OTHER. 